For what purpose is the _isAllowed() method used and which class types implement it

isAllowed() is a method of Zend_Acl which is primary used to check if a “role” has access to a “resource” and a particular “privileged” in that resource.
This is mainly used in magento admin to check if admin user has access to a page.
The code is implemented in ‘admin/session’ model, which has the isAllowed() method.